1. Field of the Invention
The present invention relates to a light source device and a projection display apparatus provided with such a light source device.
2. Description of the Related Art
In recent years, large-screen display apparatuses are rapidly becoming popular. Meetings, presentations, seminars and the like using such display apparatuses are becoming common.
As display apparatuses, various kinds of displays are known such as LCDs (Liquefied Crystal Displays) and PDPs (Plasma Display Panels). They are appropriately selected depending on a size of a room where such a display apparatus is used or the number of people attending such a meeting, presentation, seminar and the like. Among them, projectors are the most widespread large-screen display apparatuses, since they are not so expensive and superior in their portability (that is, they are light, small and portable).
In such a background, recently, situations and occasions involving communications are more increasing. For example, many offices are provided with small meeting rooms, or meeting spaces or cubicles divided with partitions or the like, where meetings involving projectors are often held.
Furthermore, even in the case that there is no vacant meeting room and the like, for example, urgent needs for meetings utilizing available spaces such as aisles while projecting information slides or images on walls of such available spaces by means of projectors are becoming more common.
As a typical example of projectors, there is known a so-called DLP (registered trademark) type projector provided with a display device such as a DMD (Digital Micromirror Device) capable of modulating irradiation light by, with PWM driving, rapidly switching on/off angles of each of micromirrors which are pixels arranged in a matrix, depending on image data.
In the DLP type projector, owing to the high speed operation of the DMD, color images such as R (red), G (green) and B (blue) color images can be switched at a certain time interval to be sequentially displayed. Thus, it has an advantage in downsizing.
In such a projector, for example, a high intensity discharge lamp (HID lamp) such as an extra high pressure mercury lamp was conventionally used as a light source. Recently, however, solid state light emitting devices such as red, green and blue LEDs are used as light sources. Furthermore, fluorescent materials using the light emitted from such solid state light emitting devices as excitation light to emit light in another wavelength range are also used as light sources. Products using such light sources have been launched onto the market.
For example, Japanese Patent No. 4662185 discloses a light source device provided with a solid state light source for emitting visible light, a fluorescent layer for converting the visible light emitted from the solid state light source into visible light in another wavelength range, and a transparent base material or substrate, as well as a projector using such a light source device.
In prior arts such as Japanese Patent No. 4662185, however, fluorescent materials for all colors to be displayed are arranged or applied on a fluorescent wheel in a circumferential direction, and the fluorescent wheel is irradiated with the excitation light all the time. Therefore, fluorescent materials are heated to decrease the luminous efficiency, so that a high quality image is not displayed. Otherwise, the time degradation of fluorescent materials is accelerated to shorten the lifetime thereof.
In order to solve the above problems, technologies are disclosed by Japanese Patent Application Laid-open No. 2011-95391 and Japanese Patent Application Laid-open No. 2011-95392. These technologies use projector light sources individually for each color required to be displayed. Thus, fluorescent wheels are provided individually for each color. Each fluorescent wheel emits only a predetermined wavelength of light specific to the excitation light irradiated thereto. Thus, there is no need to irradiate the fluorescent wheel with the excitation light all the time. Therefore, it is intended to prevent or reduce the decrease of the luminous efficiency due to the heated fluorescent materials.
Furthermore, in Japanese Patent Application Laid-open No. 2011-95391, the emission timing of the excitation light and the rotation speed are controlled, so that a spot or region on the fluorescent wheel irradiated with the excitation light is shifted with time. To the contrary, in Japanese Patent Application Laid-open No. 2011-95392, the emission duration time of the excitation light is controlled so as to synchronize with N rotations (N is an integer) of the fluorescent wheel. Thus, in both cases, it is intended to prevent the time degradation of fluorescent materials by irradiating uniformly the whole fluorescent wheel with the excitation light.
However, technologies disclosed in Japanese Patent Application Laid-open No. 2011-95391 and Japanese Patent Application Laid-open No. 2011-95392 both have a following problem. If the fluorescent layer formed on the wheel has any defect region partially which may affect the image display quality, the image display quality may be deteriorated because of such a defect region.